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A144848
a(n) = number of distinct prime divisors (taken together) of numbers of the form x^2+1 for x<=10^n.
4
7, 70, 720, 7102, 70780, 704537, 7026559, 70122424, 700184485, 6993568566, 69870544960, 698175242376
OFFSET
1,1
MATHEMATICA
d = 10; l = 0; p = 1; c = {}; a = {}; Do[k = p x^2 + 1; b = Divisors[k]; Do[If[PrimeQ[b[[n]]], AppendTo[a, b[[n]]]], {n, 1, Length[b]}]; If[x == d, a = Union[a]; l = Length[a]; d = 10 d; Print[l]; AppendTo[c, l]], {x, 1, 10000}]; c (* Artur Jasinski *)
CROSSREFS
For primes of the form n^2+1 see A002496.
Sequence in context: A299870 A196662 A249750 * A292841 A180902 A078246
KEYWORD
nonn
AUTHOR
Artur Jasinski & Bernhard Helmes (bhelmes(AT)gmx.de), Sep 22 2008, Sep 24 2008
EXTENSIONS
Fixed broken link and extended to agree with website. - Ray Chandler, Jun 30 2015
STATUS
approved